For both Republicans and Democrats up for reelection in 2012, competing proposals on federal spending form a risky dilemma.

Reporting from Washington — — Senators expecting tough reelection challenges in 2012 struggled Tuesday to decide between competing proposals that would cut federal spending this year, as legislative leaders set votes as part of the effort to fend off another threatened government shutdown.

Democratic and Republican senators measured their choices in public and private. For some, the House-passed GOP budget plan, with the deepest spending cuts in generations, goes too far in slashing jobs and programs. The more modest White House-backed proposal is too timid for those facing angry voters clamoring for limits on Washington spending.

"Cuts. They want cuts," said Sen. Ben Nelson (D-Neb.), speaking about voters back home. "But they want them fair and they want the discussions back here to be serious about cuts and not political gimmicks."

Nelson, among the more endangered of the Democrats whose terms expire in 2012, had yet to disclose his decision.

"That's what we've wrestled with," Nelson said.

Both Republican and Democratic senators up for reelection next year face a political squeeze over the budget standoff. By backing the House-passed plan, they face anger from voters who oppose such deep cuts. But opposing it could bring a mobilized response from conservative voters.

The dilemma affects Senate Democrats such as Nelson, Claire McCaskill of Missouri, Jon Tester of Montana, Debbie Stabenow of Michigan and others. Republicans potentially caught up in the issue include Olympia J. Snowe of Maine, Richard G. Lugar of Indiana and Scott Brown of Massachusetts.

The Senate was to vote Wednesday on the competing measures. Both are expected to fail, but the outcome will help define a middle ground in sharply divided talks. All sides have said they want to avoid a government shutdown after March 18, when a short-term spending deal expires.

Democrats have begun to argue that increased tax revenue, not just cuts, must be part of the equation, possibly through closing loopholes. The GOP-led House bill would slash more than $60 billion in the remaining seven months of fiscal 2011, cutting deeply into government programs in every state, including funds for Head Start preschools, law enforcement and infrastructure projects.

Several senators up for reelection next year declined to say how they would vote.

Lugar set off a controversy when he first told reporters he opposed his party's bill, then emerged from a party meeting to announce his support for it. A spokesman said Lugar had misunderstood a question about his position, but that didn't stop the criticism from a "tea party" challenger in Indiana.

The influential group Tea Party Patriots initiated a phone campaign to pressure Snowe, who is likely to face a right-flank primary challenge, to vote for the GOP bill.

Republican campaign committees were poised to attack Democrats who vote against the House measure, casting them as out of touch with voters. McCaskill, who plans to vote against the GOP plan, is likely to be on the receiving end of such a campaign.

But Democrats are planning similar attacks.

As the two sides remain $50 billion apart, Democratic Sen. Joe Manchin III of West Virginia, who could face a tough reelection in 2012, made a public display of his disappointment in both bills, insisting President Obama must negotiate an end to the stalemate. "The president must lead," he said in a speech on the Senate floor.

Talks continued behind the scenes between leaders and the White House. Vice President Joe Biden, tapped by the president to lead the negotiations, was receiving "frequent updates" as he traveled in Russia, a White House aide said.